Different IgM+ B cell subpopulations residing within the peritoneal cavity of vaccinated rainbow trout are differently regulated by BAFF. Issue 85 (February 2019)

• Record Type: Journal Article
• Authors: Granja, Aitor G.; Tafalla, Carolina
• Is Part Of: Fish & shellfish immunology. Issue 85(2019)
• Page Start: 9
• Page End: 17
• Publication Date: 2019-02
• Subjects: Rainbow trout -- Peritoneum -- B cell -- Plasma cell -- BAFF -- BAFF receptors; Fishes -- Immunology -- Periodicals; Shellfish -- Immunology -- Periodicals; Poissons -- Immunologie -- Périodiques; Crustacés -- Immunologie -- Périodiques; 571.9617
• DOI: 10.1016/j.fsi.2017.10.003
• Languages: English
• ISSNs: 1050-4648

Abstract

Abstract: In teleost fish, IgM + B cells are one of the main responders against inflammatory stimuli in the peritoneal cavity, as IgM + B cells dominate the peritoneum after intraperitoneal stimulation, also increasing the levels of secreted IgM. BAFF, a cytokine known to play a major role in B cell biology, has been shown to be up-regulated along with its receptors in the peritoneum of rainbow trout upon antigenic exposure, however, the regulatory mechanisms underneath this response remain unclear. In this study, we have identified two different IgM + B cell types residing in the peritoneal cavity of previously vaccinated rainbow trout ( Oncorhynchus mykiss ): IgD + IgM hi MHCII hi cells, resembling naïve B cells, and IgD − IgM lo MHCII lo cells, resembling antibody-secreting cells. Based on their membrane IgM levels, these cell types were named IgM hi and IgM lo B cells, respectively. As each of these B cell populations showed a distinct expression pattern for the different BAFF receptors, we studied the effect of BAFF individually on each cell subset. Recombinant BAFF promoted the survival of IgM lo but not IgM hi B cells in vitro, resulting in increased levels of IgM-secreting cells. In contrast, BAFF increased the levels of membrane MHC II only on IgM hi B cells, suggesting different functions on these B cell subsets. Moreover, we also showed that peritoneal IgM hi B cells expressed BAFF at levels comparable to those seen on myeloid cells. These results point to BAFF as a main regulator of B cell homeostasis in the peritoneal cavity, suggesting that this cytokine can trigger different signals on different peritoneal B cell subsets in a specific manner. Highlights: Two different populations of IgM + B cells, IgM hi and IgM lo, coexist in the peritoneal cavity of vaccinated fish. IgM hi B cells resemble naïve B cells while IgM lo resemble IgM secreting plasma cells. BAFF increases the survival of peritoneal IgM lo B cells, leading to an increased IgM secretion. BAFF increases the level of membrane MHC II on IgM hi but not on IgM lo peritoneal B cells. IgM hi B cells produce BAFF, pointing to an auto-regulatory mechanism of B cell survival in the peritoneum.